It was first revealed in Third Wheel; Ted reveals that he and Barney have a running joke that the first one between them to be in a three will win the championship belt. Marshall thinks he means a metaphorical belt, but it's shown that Barney went out and actually got the WWF "Winged Eagle" championship title belt for the occassion. The belt is mentioned many times throughout the series, and in the Barney's Blog entry From The Files Of Li'l Barney. In that episode Ted enters the bedroom where Trudy and Rachel are, but later he doesn't reveal if he had won the belt.